Quick Summary

Common Mounjaro side effects include nausea, vomiting, diarrhoea, and constipation. Most are mild and temporary, occurring most often when starting treatment or increasing dosage. Side effects typically improve within a few days to weeks as your body adjusts.

Mounjaro Side Effects: What to Expect

Medical Review: Reviewed by registered pharmacist. Last Updated: December 2025. Location: Glasgow, Scotland.

Common Side Effects

Like all medications, Mounjaro can cause side effects. Most side effects are mild and temporary, occurring most often when you first start treatment or when your dose is increased. Understanding what to expect can help you manage side effects effectively.

Most Common Side Effects

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Nausea: Feeling sick to your stomach, especially after eating. Usually mild and improves over time.
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Vomiting: Less common than nausea, usually occurs if you eat too much or too quickly.
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Diarrhoea: Loose or watery stools. Usually temporary and improves as your body adjusts.
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Constipation: Difficulty passing stools. Can be managed with diet and hydration.
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Abdominal Pain: Stomach discomfort or cramping, usually mild.
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Decreased Appetite: This is actually the intended effect, helping with weight loss.

Less Common Side Effects

Some patients may experience:

Fatigue or tiredness
Dizziness
Indigestion or heartburn
Injection site reactions (redness, itching)
Headache

When Side Effects Occur

Side effects are most likely to occur:

During the first few weeks: As your body adjusts to the medication
When increasing dosage: Each dose increase may cause temporary side effects
After eating large meals: Eating too much can worsen gastrointestinal side effects
With certain foods: Fatty, rich, or spicy foods may increase side effects

Managing Side Effects

Most side effects can be managed with simple strategies:

For Nausea

Eat smaller, more frequent meals
Avoid fatty, greasy, or spicy foods
Eat slowly and chew thoroughly
Stay hydrated with water or clear fluids
Consider ginger tea or ginger supplements

For Diarrhoea

Stay well hydrated
Eat bland foods (bananas, rice, toast)
Avoid dairy and high-fibre foods temporarily
Contact your pharmacist if it persists

For Constipation

Increase fibre intake gradually
Drink plenty of water
Stay physically active
Consider over-the-counter remedies if needed (consult pharmacist first)

When to Seek Help

Contact your pharmacist or seek medical attention immediately if you experience:

Severe abdominal pain: Especially if persistent or worsening
Signs of pancreatitis: Severe upper abdominal pain, nausea, vomiting
Severe allergic reaction: Rash, hives, difficulty breathing, swelling
Persistent vomiting: Unable to keep fluids down
Severe diarrhoea: With signs of dehydration
Any concerning symptoms: When in doubt, contact your pharmacist

Frequently Asked Questions

What are the most common side effects of Mounjaro?

The most common side effects include nausea, vomiting, diarrhoea, constipation, and abdominal pain. These are typically mild and temporary, occurring most often when starting treatment or increasing dosage.

How long do Mounjaro side effects last?

Most side effects are temporary and improve within a few days to weeks as your body adjusts to the medication. Side effects are most common during the first few weeks and when increasing dosage.

What should I do if I experience severe side effects?

If you experience severe or persistent side effects, contact your pharmacist immediately. Seek emergency medical attention if you experience severe abdominal pain, signs of pancreatitis, or allergic reactions.

Can I reduce Mounjaro side effects?

Yes, side effects can often be managed by starting at a low dose, increasing gradually, eating smaller meals, staying hydrated, and avoiding fatty or rich foods. Your pharmacist will provide guidance on managing side effects.

Do side effects mean the medication isn't working?

No, mild side effects are actually a sign that the medication is working. The same mechanisms that cause side effects (slowing digestion, reducing appetite) are what help with weight loss.